Filter medium, filter element and use thereof and filter arrangement

ABSTRACT

A filter medium ( 10 ) for filtering a fluid, in particular for use in an interior air filter ( 32 ), comprises a spun-bonded nonwoven formed at least in part of multi-component segmented pie fibers ( 1 ) having at least a first plastic component ( 2 ) and a second plastic component ( 3 ). The multi-component fibers ( 1 ) are largely non-split, and in order to manufacture same, segmented pie filaments are spun in a spun-bonding process (S 4 ) to form a spun-bonded nonwoven ( 10 ). The segmented pie filaments then form the multi-component fibers ( 4 ), the first plastic component ( 2 ) and/or the second plastic component ( 3 ) being made in particular of a polypropylene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of internationalapplication No. PCT/EP2018/057973 having an international filing date of28 Mar. 2018 and designating the United States, the internationalapplication claiming a priority date of 28 Mar. 2017 based on priorfiled German patent application No. 102017002957.1, the entire contentsof the aforesaid international application and the aforesaid Germanpatent application being incorporated herein by reference to the fullestextent permitted by the law.

TECHNICAL FIELD

The present invention relates to a filter medium, a filter element anduses thereof and a filter arrangement.

When filtering fluid media, such as air for the interior of a vehicle orbuilding, filter media are used. Known filter media are, for example,papers, foams, fabrics and nonwovens, which are also referred to asnonwoven materials. The present invention relates to nonwovens andcombinations with nonwovens as filter media.

Although filter media are conceivable for various fields of application,in the present case, particular attention is given to the problem offiltering in the area of HVAC (Heating, Ventilation and AirConditioning) and of supply air for the interior of a motor vehicle.However, the described filter elements and filter media may also be usedin other applications, for example as a filter for fuel cells, for fansor for switch cabinets or serve as a suction filter for engines orcompressors.

Filter media are processed in the manufacture of filter elements, forexample, filter media are laminated, embossed, pleated, pleated or cut.For these processing steps, the filter media must be suitable. Likewise,filter media for further processing steps such as injecting, foaming orfoam-coating, gluing or bonding must be suitable.

The increasing air pollution, especially in large cities, in connectionwith the use of modern air conditioners makes it necessary that, forexample, the treated or conditioned air which is conducted into theinterior of a motor vehicle or a house be purified by means of suitablefilters. For this purpose, for example, particulate filter, odor filteror their combination with each other come into consideration, whichshould filter or adsorb suspended solids, particulate matter and odorscontained in the ambient air as well as possible.

For filtering air, in particular for the interior of a motor vehicle,pleated or pleated filter media, which form a pleat pack, are frequentlyused. For this purpose, an initially flat filter material sheet ispleated in a zigzag or wavy shape. The pleat pack is held, for example,by sidebands and headbands or another frame. Such filter elements can befixed exchangeably in a filter holder. The filter assembly formedthereby may be in an air conditioner of a corresponding motor vehicle.The formation of pleats can maximize the filter area in a given size andthereby lower the media speed and the flow rate through the filtermedium. As a result, for example, a lower flow resistance and a higherfiltration efficiency can be achieved or service life can thereby beincreased.

BACKGROUND

In principle, nonwovens are known as filter media. Depending on theapplication, the filter medium requires a certain rigidity, a certainretention capacity for particles in the fluid to be filtered, a certainpermeability or a certain pressure loss and certain material properties.For example, nonwoven composites have been proposed, which aresolidified by means of a hydroentanglement and are mounted on a supportstructure. DE 10 2011 009 227 A1, for example, discloses a method forproducing a corresponding nonwoven in which a hydro-dynamic needling isachieved in order to produce wet or dry felts.

EP 2 479 331 B1 proposes to split multi-component fibers, which areprocessed as spun-bonded nonwovens, in order to obtain a particularlyfine fiber structure. In this case, multilayer nonwovens are produced inparticular for use in hygiene products.

From US 2002/0013111 A1, splittable polyester fibers of severalcomponents are known. The fibers are processed and needled as staplefibers into a flat material. According to US 2002/0013111 A1, ahydrodynamic entanglement with water jets is performed, which split theseveral components of the individual fibers and wherein particularlythin and fine fiber structures arise.

Often nonwovens also contain bicomponent fibers as so-called core-sheathfibers. For example, US 20070220852 A1 describes a spun-bonded nonwovenhaving core-sheath fibers as binder fibers as the filter medium. Here,the core has, for example, a higher melting point than the sheath, sothat by heating to the softening or melting temperature of the sheath, acompound of the binder fibers with each other and with other fibers ofthe nonwoven is made possible and thereby a stable nonwoven is achieved.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide animproved filter medium based on a spun-bonded nonwoven, in particularfor use as an interior air filter, e.g. in vehicles, or in the area ofHVAC, for example in building technology. It is a further object toprovide an improved or alternative filter element for a filterarrangement.

Filter Medium: Geometry

Accordingly, a filter medium for filtering a fluid with a spun-bondednonwoven is proposed, which is formed at least partially from segmented,in particular multi-component segmented pie fibers with at least onefirst plastic component and a second plastic component.

Multi-component segmented pie fibers are also known in the literatureand technology as segmented pie fibers. If multi-component fibers haveessentially two components, they are referred to as bicomponent fibers.Other configurations of multi-component fibers are, for example, coresheath fibers in which a core of one component is surrounded by a sheathof another component. Side-by-side configurations of multi-componentfibers are also known.

The flat filter medium is particularly suitable for use in an interiorair filter for supplying air in a motor vehicle or in HVAC applications.It has been found that multi-component segmented pie fibers obtained bya spun-bonding process have favorable filtration properties.Multi-component fibers may also be referred to as poly or multicomponentfibers.

By “segmented” it is meant that there are interfaces between the variousplastic components substantially along the length extension of thefibers. It is not excluded that further segments or plastic componentsextending along the length extension are present within themulti-component fibers. In the cross-section of a correspondingmulti-component fiber, it results in a view in the manner of pie pieces,which are formed of different plastic components.

In principle, it is conceivable that the term “plastic component” doesnot mean that the segments have different compositions. Interfacesbetween the segments could also be generated by the production process.In the context of this invention, however, the term plastic componentdescribes the composition of the material of a segment, and in the caseof a multi-component fiber at least two different compositions arepresent.

In embodiments, the multi-component fibers of the spun-bonded nonwovenused as a filter medium have a substantially pie-shaped cross-section.In comparison to conventional spun-bonded nonwovens in which themulti-component fibers are essentially split when used as a filtermedium. There, the fiber sections resulting from the components usuallyhave an irregular, for example, triangular cross-section.

In embodiments of the filter medium, a respective multi-componentsegmented pie fiber has a sheath surface, and the plastic componentsadjoin one another on the sheath surfaces of the multi-component fibers.

In embodiments, the sheath surface has longitudinal grooves alonginterfaces between the plastic components of a respectivemulti-component fiber. For example, the longitudinal grooves may resultin the manufacturing process by melting or due to the surface tension ofthe still liquid plastic material during spinning. Substantially, arespective multi-component fiber may have a smooth surface. For example,it is conceivable that the sheath surface has an average roughness depthof less than 2 μm along a circumference.

The boundary layers or interfaces between the plastic componentsextending along the length extension of the multi-component fibers canlead to an improved filtering effect. Electrical charges or geometrictransitions, such as edges or grooves, can improve the collection ofparticles from the fluid to be filtered.

Depending on the desired properties of the filter medium, themulti-component segmented pie fibers can be present in different fiberthicknesses. In certain embodiments of the filter medium, themulti-component segmented pie fibers have an average diameter of between10 μm and 40 μm, preferably between 15 μm and 30 μm.

In other embodiments, the average diameter is between 20 μm and 60 μm,and is preferably between 30 μm and

40 μm.

In the proposed multi-component fibers, the respective first and secondplastic components adhere to one another and, as a whole, form thesegmented pie fiber. Known filter media comprising multi-componentfibers which are split, felted or needled tend to have smaller meandiameters.

In embodiments, the multi-component segmented fibers include at leastfour, six, or eight pie segments. 16 pie segments are preferred, but ahigher number of pie segments is also possible. For example, at 16 piesegments along the length of a respective multi-component fiber, thereare also 16 interfaces of the plastic components to one another. Theseinterfaces may be beneficial to the filtration properties. However, thenumber of interfaces must be weighed against an efficient productionprocess.

The multi-component fibers can be designed so that they do not splitapart under the influence of a water jet treatment. For example, a goodadhesion of the same can be adjusted to one another by the choice of theplastic components. By obtaining the multi-component fibers as non-splitfibers, the filter media becomes robust and, on the other hand,particularly efficient.

However, a water jet treatment or another treatment which results in thesplitting of the multi-component fibers or a majority of themulti-component fibers can also be avoided in the production of thenonwoven and its processing to the filter element. In other words,according to the invention it is also a spun-bonded nonwoven from amulti-component fiber in a segmented pie configuration, which is used asa filter medium without being hydroentangled.

In embodiments, a proportion of multi-component fibers in the filtermedium, in which the pie segments are interconnected at inner segmentboundaries of the multi-component fibers along their length extension,is at least 50%. Preferably, at least 70% of the multi-component fibersare correspondingly non-split, and more preferably at least 80%. Theproportion can be determined, for example microscopically, by examiningfibers from a predetermined area of the spun-bonded nonwoven with regardto the splitting of their plastic components.

In embodiments of the filter medium, with a length fraction of themulti-component fibers of not more than 50%, the pie segments of themulti-component fibers are split from one another. Preferably, less than30% of the multi-component fibers are split in length, and morepreferably at most 20% of the multi-component fiber length is split. Ina length fraction, a respective fiber or a fiber section can beexamined, and the length fraction of contiguous pie segments can bechecked with the length fraction of pie segments split apart from oneanother. This results in the length fraction of the multi-componentfibers that are split or non-split.

In embodiments of the filter media, the multi-component fibers of thespun-bonded nonwoven are oriented along the machine direction. Themachine direction results, for example, by depositing spun-bondednonwoven filaments on a movable storage screen belt.

In the filter medium, the plastic components are interconnected. Theplastic components are interconnected in a spun-bonding process. It isalso conceivable that the plastic components or segments are partiallyfused together in areas of the boundaries between the first and thesecond plastic component. This can result in a particularly goodadhesion of the segments together.

In embodiments, the filter medium or the multi-component fibers areconnected to one another by means of a hot air bonding, in particularexclusively interconnected to one another by means of a hot air bonding.The spun-bonded nonwoven then has a thickness between 1.0 and 2.0 mm.Preferably, the thickness is between 1.2 and 1.8 mm, and more preferablybetween 1.3 and 1.7 mm. With a thickness of between 1 and 2 mm, afavorable further processability of the pre-solidified spun-bondednonwoven, which can also be referred to as semi-finished product,results, for example, for further densification or solidification.

In embodiments of the filter medium, the multi-component fibers arebonded together under thermal exposure to form a nonwoven. This can beachieved, for example, by irradiation of heat or hot air on thespun-bonded nonwovens running on screen belts. The spun-bonded nonwovenhas, for example, a thickness between 0.5 and 1.5 mm, preferably between0.8 and 1.3 mm, after the additional thermal exposure. By densificationor solidification of the medium initially provided as a nonwoven, animproved mechanical resistance is achieved.

The stated thicknesses provide good filtration properties for acorresponding spun-bonded nonwoven with preferably non-split or mostlynon-split multi-component fibers. For example, the number of interfacesbetween different plastic components plays a role, as well as thedistance from corresponding interfaces between different fibers in thespun-bonded nonwoven.

In further embodiments of the filter medium, the spun-bonded nonwovenhas pleats with a plurality of pleating sections arranged between pleatedges. The spun-bonded nonwoven, due to its mechanical properties andthe multi-component fibers which are at least partially, preferablymostly, non-split, has a good form stability, which is suitable forpleating. The pleats can preferably run transversely to the machinedirection, so that oriented fibers are pleated or kinked in theirlength.

Filter Medium: Physical Properties

In embodiments, the plastic components of the multi-component fibers arecharged as electrets. That is, charges are accumulated on the plasticcomponents. It is conceivable that the different plastic components,although they may have the same material composition, have a differentcharge configuration. As a result, in particular at the boundarysurfaces of the pie segments, a special electric field configurationresults, which can have an advantageous effect on the filtrationproperty.

The filter medium comprises in embodiments a spun-bonded nonwoven with agrammage

between 80 and 160 g/m². The so-called grammage is measured inparticular according to DIN 29073-1. Preferably, the grammage may bebetween 90 and 110 g/m². In other embodiments, the grammage is setbetween 80 and 100 g/m², and in still other embodiments between 110 and150 g/m².

In embodiments, the spun-bonded nonwoven in particular has a flexuralrigidity of greater than 170 mN, preferably greater than 180 mN, andmore preferably greater than 200 mN. A measurement of the flexuralrigidity is carried out in particular according to DIN 53121 accordingto the beam method with a modified flexural angle of 15°. The use ofmultiple-component fibers, preferably in a segmented pie configuration,preferably as bicomponent fiber, which are partially, preferablypredominantly, non-split and thermally solidified, results in a goodflexural rigidity of the filter medium, which simplifies furtherprocessing, for example in filter elements, and at the same time resultsin a good air permeability.

The filter medium may further comprise a meltblown material inembodiments. A spun-bonded nonwoven according to the invention canserve, for example, as a carrier for a meltblown material, a meltblownnonwoven, and together with this form a multilayered filter medium.Different combinations of meltblown fabric layers and spun-bondednonwoven layers are conceivable.

In one embodiment of the filter medium according to the invention, thespun-bonded nonwoven is provided with the at least partially, preferablymostly non-split, multi-component segmented pie fibers, preferablybicomponent fibers with a microfiber layer, in particular with ananofiber layer, i.e. a layer in which the average fiber diameter isless than 1 μm.

Other embodiments with combinations of the spun-bonded nonwovenaccording to the invention with meltblown layers and ultra-fine fiberlayers are, of course, conceivable.

It is also possible for the filter medium to comprise adsorberparticles, for example activated carbon or other adsorber materials, forfiltering or adsorbing volatile substances. The filter medium issuitable for removing hydrocarbons from air to be filtered.

In particular, activated carbon can be applied to the spun-bondednonwoven according to the invention and can be fixed with a furtherlayer, for example a meltblown nonwoven or with adhesive threads oradhesive dots. Such a layer can be covered with further layers, forexample one or more meltblown fabrics or even one or more spun-bondednonwovens.

Filter Medium: Material Compositions

In embodiments of the filter medium, the first plastic component and/orthe second plastic component consist(s) of a polypropylene. It isadvantageous that the first plastic component has a first melting pointand the second plastic component has a second, different, melting point.The first melting point is then preferably higher than the secondmelting point, and between the first and the second melting point is adifference of at least 8 K. Preferably, the difference in melting pointsis at least 10K, and more preferably at least 15K.

By adjusting the melting points to each other, a favorable adhesive bondbetween the plastic components and thus the pie segments along thelength of the multi-component fibers can be achieved and a goodconnection or crosslinking of the multi-component fibers with oneanother can be achieved in the production of the spun-bonded nonwovenaccording to the invention or of the filter medium according to theinvention. The circular, pie-shaped fiber shape should also bemaintained under thermal loads, e.g. during solidification, during theproduction process.

In embodiments, the mass fraction of the first plastic component isbetween 60 and 80%, preferably between 65 and 75%. By changing the massfraction of the plastic component, mechanical properties of themulti-component fibers can be determined. Of course, the plasticcomponents may also comprise mixtures and blends of a plurality ofplastic materials, for example a plurality of thermoplastic materials.

In embodiments of the filter medium, the first plastic component and/orthe second plastic component has/have a first portion of a firstthermoplastic material having a first melting point and a second portionof a second thermoplastic material having a second melting point. Byselecting the proportions of the first and second thermoplasticmaterial, the resulting melting points for the plastic components orother properties such as viscosity can be adjusted. This facilitates theproduction in the spinning process.

In embodiments of the filter medium, in particular one of the twoplastic components of different multi-component fibers for solidifyingthe spun-bonded nonwoven is partially fused together. For example, it ispossible for a plastic component having the lower melting point withinthe fibers to fuse upon thermal solidification and fibers to adhere toeach other, thereby forming a fiber network.

In embodiments, the first thermoplastic material is a polypropylenehomopolymer. The second thermoplastic material may then be in particulara metallocene polypropylene. It is also conceivable that the first orsecond thermoplastic material is a co-polypropylene.

In embodiments, the sheet spun-bonded nonwoven in a respective area of10 cm² has a rigidity such that it is self-supporting. The spun-bondednonwoven is in particular thermally made more rigid. By“self-supporting”, it is understood that the area of 10 cm2 does notsag, deflect or break under the weight.

Filter Medium: Filtration Properties

The spun-bonded nonwoven of the filter medium in embodiments has an airpermeability at 200 Pa of between 500 l/m²s and 6000 l/m²s. The airpermeability is measured in particular according to EN ISO 9237.

In embodiments, the spun-bonded nonwoven has a NaCl retention capacityat 0.3 μm particle size of greater than 10%. In embodiments, a NaClretention capacity of greater than 30%, and preferably greater than 40%,is achieved. In particularly preferred embodiments, the spun-bondednonwoven has a NaCl retention capacity of greater than 50%. Theretention capacity is, for example, determined according to DIN 71460-1.

But also spun-bonded nonwovens can be provided, for example as a carriermaterial in a filter medium, in which the NaCl retention capacity isless than 10%.

In embodiments, the spun-bonded nonwoven has a dust holding capacitywith a differential pressure increase of 50 Pa of greater than 20 g/m²,preferably greater than 30 g/m². In embodiments, dust storage capacitiesof more than 40 g/m², and preferably more than 50 g/m², may also beachieved at 50 Pa. The dust storage capacity is, for example, determinedaccording to DIN 71460-1.

A particularly open filter medium may be adapted to remove particles ofthe test dust according to ISO 12103-1 from an air stream with afiltration speed of 0.10 to 0.30 m/s, based on the filter mediumsurface, with an air permeability of more than 3000 l/m²s (determinedaccording to ISO 9237 at 200 Pa). The filtration characteristics can bedetermined, for example, according to DIN 71460-1.

A filter medium of particularly high arrestance may be adapted to passparticles of the test dust according to ISO 12103-1, as well as NaClaerosol particles according to DIN 71460-1, from an air stream with afiltration speed of 0.10 to 0.30 m/s, based on the filter mediumsurface, with an air permeability of more than 600 l/m²s (determinedaccording to ISO 9237 at 200 Pa). The filtration characteristics can bedetermined, for example, according to DIN 71460-1.

Filter Elements: Construction

In embodiments, a filter element comprises a spun-bonded nonwoven asfurther described hereinbefore or hereinafter which is formed at leastin part of multi-component segmented pie fibers having at least a firstplastic component and a second plastic component, wherein a portion ofmulti-component fibers whose pie segments are interconnected at innersegment boundaries of the multi-component fibers along their lengthextension, is at least 50%, preferably 70%, more preferably 80%.

In a further embodiment, the proportion of the multi-component segmentedpie fibers on the spun-bonded nonwoven is more than 50%, preferably morethan 80%.

In particular, the filter element may comprise a filter medium having aspun-bonded nonwoven as described above or below. The filter medium ispreferably pleated into a pleat pack in a zigzag shape. By pleating in azigzag shape, the total filter surface contained in the pleat pack isincreased.

Due to the mechanical properties of the spun-bonded nonwoven, whichresult in particular from the largely non-split multi-component fibersin the manner of segmented pie fibers, an easily handled and processablepleat pack can be produced.

In embodiments of the filter element, said filter element comprisessidebands on opposite pleat profiles of the pleat pack. Headbandsmounted on opposite end pleats of the pleat pack may also be provided.Due to the fibers used and the resulting stability, such as rigidity andseparation efficiency of the filter medium, it is also possible to formfilter elements which have no end pleat reinforcement or headbands. Thisis created by a simple and inexpensive producible filter element.

The filter element comprises, for example, the proposed spun-bondednonwoven as a filter medium or filter material and one or morestabilizing elements, in particular sidebands and/or headbands (alsoreferred to as frontlets), which stabilize the filter medium at least insections, in order to maintain its shape, in particular in the filteroperation. The stabilizing elements can in particular form a closed oropen frame—also in one piece of material—which surrounds the filtermedium.

Alternatively or in addition to the filter medium, the stabilizerelement(s), for example the sidebands and/or headbands referred toherein, may comprise the spun-bonded nonwoven. As an alternative or inaddition, other apparatus components of the filter element according tothe invention may also comprise the spun-bonded nonwoven.

The stabilizing elements can be materially connected to the edge of thefilter medium, in particular adhesively bonded or welded. For thispurpose, the stabilizing elements can be heated and the filter media arepressed into the heated material. Alternatively, the stabilizingelements may be molded onto the filter medium. Furthermore, an adhesivemay be used as

filler material. The stabilizing elements may themselves be made of thesame material as the filter medium. Alternatively, the stabilizingelements may be formed as synthetic injection molded components. Thestabilizing elements can be rigid or flexible.

The filter element may further comprise a seal which seals a raw sideassociated with the filter element with respect to a clean side thereof.The seal may be identical in construction to one or more stabilizingelements of the filter element. Alternatively, the seal may be formed asan additional component. For example, the seal may be attached to thefilter medium, the one or more stabilizing elements, the filter elementor the filter holder.

The filter medium can be pleated or even wavy. For example, zigzag M orW pleats are known as pleats. The filter medium can be embossed and thenpleated sharp-edged at embossing edges to form pleating edges. Thestarting material used is a flat material sheet of the spun-bondednonwoven, which is correspondingly re-shaped. Furthermore, the filtermedium can additionally be felted or needled. The filter medium mayhave, in addition to the spun-bonded nonwoven, natural fibers such ascotton, or synthetic fibers, for example of polyester, polyphenylsulfideor polytetrafluoroethylene. The respective fibers may be oriented in,skewed and/or transversely to the machine direction during processing.

Furthermore, the filter medium may have an antimicrobial and/orantiallergenic effect. Zinc pyrithione or nanosilver, for examplepolyphenol as an antiallergenic substance, is considered as anantimicrobial substance.

Filter Elements: Applications

A corresponding filter element serves to filter fluids, i.e. gaseousand/or liquid media, for example air. A gaseous medium or air hereinalso includes gas-solid or air-solid mixtures and/or gas-liquid orair-liquid mixtures. For example, an air conditioner may have the filterelement.

In embodiments, the filter element is an interior air filter element fora motor vehicle. The filter element is usually a replacement part thatis changed after a certain lifetime. The favorable properties of thefilter medium with respect to the filter characteristics and themechanical properties allow a prolonged use, or period of use at a highfiltration performance.

The filter element or the filter assembly can be used in passenger cars,trucks, construction machines, watercraft, rail vehicles, aircraft andin general in air conditioning technology, especially in airconditioning appliances, in household appliances, office equipment, suchas computers, printers or copiers, in fuel cells or in buildingtechnology. These passenger cars or vehicles can be operatedelectrically and/or by means of fuel (especially petrol or diesel). Interms of building technology, in particular stationary or mobilefacilities for the treatment of air come into consideration. In internalcombustion engines, but also in compressors, cleaning of the intake airfor both the combustion air and for the air that is to be compressedwith the filter element is possible.

Filter Elements: Shape

The filter element has, for example, outer boundary surfaces enclosing acuboidal volume. As a rule, the pleating edges of the pleat pack havethe largest boundary surface, and the pleat height or pleat depthdetermines the size of the other boundary surfaces.

The two, in particular largest, boundary surfaces have in each case anarea between 0.05 and 0.066 m². For example, the length of the largestboundary surface is between 290 and 295 mm, and the width is 196 to 201mm. In further embodiments, the pleat pack has, for example, an upperbounding surface of between 0.053 and 0.062 m². In other embodiments,areas between 0.056 and 0.06 m² are possible.

Corresponding sizes can be filled in a favorable zigzag pleated mannerwith the help of the filter medium, so that the respective requiredfilter area is achieved. Due to the good filter medium with respect toits filter properties and its mechanical properties of the filtermaterial with the spun-bonded nonwoven of mainly non-splitmulti-component fibers, the surface can be reduced in principle with thesame filter performance over conventional filter media. This leads to amaterial saving.

In embodiments, the filter element has a filter medium with an areabetween 0.458 and 0.472 m². This area, which is preferably between 0.462and 0.47 m², can be arranged by the zigzag-shaped pleating within thepleat pack with its predetermined boundary areas. In other embodiments,the filter medium has an area between 0.464 and 0.468 m². Most pleats ofthe pleat pack are arranged transversely to the machine direction. Thepleat pack may then have, for example in the machine direction, a lengthof between 285 and 300 mm and comprise between 38 and 46 pleats. Thepleat heights are, for example, between 25 and 31 mm. Such a dimensionedfilter element shows a particularly good separation efficiency when itis equipped with the filter medium from the multi-component fibers.

Production Method

A spun-bonded nonwoven according to the invention can be produced asfollows. By means of at least one spinnerette, at least multi-componentfibers, in particular bicomponent fibers, are spun, which in particularhave a segmented pie configuration. The multi-component fibers can alsobe spun together with other fibers as a mixture of fibers. Subsequently,the multi-component fibers are cooled by means of at least one coolingapparatus, the fibers are drawn and deposited on a storage screen beltto the nonwoven web. The fabric web is subjected to hot-fluidsolidification, wherein the fabric web is thereby applied flat with hotfluid and in addition pressure is exerted extensively on the fabric webduring hot fluid application.

Preferably, hot air is applied to the nonwoven web in a firstsolidification stage on the storage screen belt. Following this, orfollowing the dropping on the storage screen belt, the nonwoven web isapplied flat with hot air in a second solidification stage, in a doublebelt furnace, wherein additionally and at the same time surface pressureis exercised on the nonwoven web. The flat pressure is applied to thenonwoven web at a pressure of between 5 and 15 Pa.

Preferably, multi-component fibers or bicomponent fibers are used inwhich a component forms more than 50% by weight, preferably more than60% by weight of the total fiber, and wherein this component preferablyconsists of a polyolefin and very preferably of a polypropylene.

The first flat hot fluid solidification on the storage screen belt canbe executed as a pre-solidification in a flow-through furnace. In thiscase, a fluid temperature is used which is below the melting point ofthe highest-melting component of the fibers and in which at least onecomponent with a lower melting point—in the case of bicomponent fibers,the component of the bicomponent fibers with a lower melting point—isfused or melted. Thus, these fibers connect at the contact points withthe adjacent underlying fibers. In this way, a transportable nonwovenweb composite is produced, which is then supplied to the secondsolidification stage. Expediently, the nonwoven web is subjected to theflow of a hot fluid, in particular hot air, in the first solidificationstage or in the first hot-fluid solidification of the hot fluid with aflow velocity of 1 to 3 m/s.

In the second solidification stage in the double belt furnace, the finalsolidification and calibration of the nonwoven web takes place. For thispurpose, the fabric web is clamped between two circulating endless beltsor screen belts, preferably between a conveyor belt and aheight-adjustable calibration belt arranged above it. With the help ofthe two screen belts, flat pressure is exerted on the fabric web, whichis flowed through or at the same time by the hot fluid or by the hotair. In the second solidification stage, the temperature is below themelting point of the component of the fibers with highest melting point.Expediently, at least one component of the fibers with lower meltingpoint—in the case of bicomponent fibers, the component with lowermelting point—is melted or partially melted. The nonwoven web is flowedin the double belt furnace by hot air with a flow velocity of 1 to 3m/s. The temperature of the hot air for the first hot-fluidsolidification and/or for the second hot-fluid solidification is atleast 100, preferably 120 to 160° C.

Following the second solidification stage or following the second hotair solidification, the nonwoven web can be electrically charged. Theelectrical charging takes place after cooling the nonwoven web in thecontext of the second hot-fluid solidification. The electrical loadingof the nonwoven web is carried out by guiding the nonwoven web by astatic electric field, wherein the electrical charging device forcharging the nonwoven web has two to three loading beams, each having 30kV. Methods and apparatus for the electrostatic charging of nonwovenmaterials are given in U.S. Pat. No. 5,401,446, to which full referenceis made herein (“incorporation by reference”). The devices of FIGS. 1 to4 of U.S. Pat. No. 5,401,446 shown therein and described are used inembodiments of the method for charging the multi-component fibers.

In a spun-bonded nonwoven produced in the spun-bonded method, the fibersare spun with the spinnerette as continuous filaments. The term “fibers”can also be replaced by “continuous filaments” or “filaments”.

In principle, it is also possible to use mixtures of the differentconfigurations of segmented pie configuration, core/shell configurationand/or a side-by-side configuration of the bicomponent filaments ormulti-component filaments. The plastic components of the multi-componentfilaments or the two plastic components of the bicomponent filamentsexpediently have in most cases different melting points.

In the case of the multi-component filaments or with bicomponentfilaments, a component forms more than 50% by weight, preferably morethan 55% by weight, preferably more than 60% by weight and verypreferably 65 to 75% by weight of the total filament.

At least one component, preferably both or all components of themulti-component filaments or bicomponent filaments, consists of apolyolefin. Conveniently, this polyolefin is polypropylene. Polyolefinblends can also be used for the components of the continuous filaments.The terms “polyolefin” and “polypropylene” also include correspondingblends of polyolefins or of polypropylenes or copolymers of polyolefinsor of polypropylenes.

The spun-bonded webs or nonwoven webs produced in this way have agrammage of between 10 and 1000 g/m2, preferably between 40 and 250g/m2.

A spun-bonded nonwoven produced according to the invention may be partof a laminate of a plurality of layers, wherein at least one layer orpart of the layers is likewise formed from spun-bonded nonwovens ornonwoven webs. Here, for example, meltblown fabrics can be used.According to a variant embodiment, the laminate or layer aggregate canhave a gradient of the fiber diameter or filament diameter with respectto the extent of its thickness. Such a laminate or layer aggregate canbe produced, in particular, by means of a plurality of spinning barsconnected in series.

In embodiments of the method, the first plastic component has a firstmelting point and the second plastic component has a second meltingpoint. The first melting point is preferably higher than the secondmelting point, and between the first and second melting points, thedifference is at least 5K. Preferably, the difference is at least 10K,or more preferably at least 12K. By setting melting points, asolidification of the spun filaments and the deposited filaments can beachieved.

In embodiments of the manufacturing method, the first and secondstarting materials are separately melted and fed to a spinning beamhaving nozzle openings. The nozzle openings are then arranged such thatsegmented filaments are formed from the first and second plasticcomponents.

In a variant of the method, a plurality of spinning beams with nozzleopenings are used.

In carrying out the method, the filaments can be stretched by means of aprimary air supply, swirled by means of secondary air supply anddeposited into a web, in particular on a screen belt.

Uses

It is further proposed to use a filter medium or spun-bonded nonwovendescribed above or below. In this respect, the use of the filter mediumor a filter element takes place for filtering a gas stream loaded withparticles. The gas stream loaded with particles may, in particular, besupply air for the interior of a motor vehicle.

In embodiments, the filter medium is used in an interior air filter fora motor vehicle.

The embodiments and features described for the proposed filter media andspun-bonded nonwovens apply to the proposed production method and viceversa.

Other possible implementations of the invention comprise combinations offeatures or embodiments described previously or in the followingregarding the exemplary embodiments, even if such combinations are notexplicitly cited. The person skilled in the art will also add individualaspects as improvements or supplements to the specific basic form of theinvention.

Further advantageous embodiments and aspects of the invention are thesubject of the dependent claims and the embodiments of the inventiondescribed below. In the following, the invention will be explained ingreater detail on the basis of preferred embodiments with reference tothe enclosed figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures are as follows:

FIG. 1: shows a schematic view of an exemplary embodiment of a filtermedium made of a spun-bonded nonwoven;

FIG. 2: shows a schematic perspective view of an exemplary embodiment ofa multi-component fiber for use in a filter medium;

FIG. 3A to 3C: show schematic cross-sectional views of furtherembodiments of multi-component fibers;

FIG. 4A to 4C: shows scanning electron micrographs of sections ofembodiments of spun-bonded nonwovens;

FIG. 5: shows a diagram for explaining a roughness depth ofmulti-component fibers;

FIG. 6: shows a schematic representation of an exemplary embodiment ofpartially split multi-component fibers;

FIG. 7: shows a schematic representation of method steps of an exemplaryembodiment for producing a web of segmented pie filaments;

FIG. 8: shows a schematic representation of method steps of anembodiment for producing a filter medium with the aid of a web, asdescribed in FIG. 7;

FIG. 9: shows a schematic sectional view of an exemplary embodiment of amultilayer filter medium;

FIG. 10: shows a schematic sectional view of a further exemplaryembodiment of a multilayer filter medium;

FIG. 11: shows a perspective view of an exemplary embodiment of a pleatpack formed from a filter medium;

FIG. 12: shows a schematic representation of a general motor vehiclewith a filter arrangement;

FIG. 13: shows a perspective view of the filter arrangement from FIG.12, comprising a filter housing with a passenger compartment filteraccommodated therein;

FIG. 14: shows a perspective view of the interior filter of FIG. 13including a frame and a pleat pack; and

FIG. 15: shows pressure difference curves for filter elements withdifferent filter media.

In the figures, identical reference signs designate identical orfunctionally equivalent elements, provided no information is provided tothe contrary.

EMBODIMENT(S) OF THE INVENTION

Spun-Bonded Nonwoven Made of Multi-Component Fibers as a Filter Medium

FIG. 1 shows a schematic view of an exemplary embodiment of a filtermedium made of a spun-bonded nonwoven. A nonwoven is a structure offibers which are joined together to form a nonwoven or a fibrous layeror a fibrous web. One also speaks of so-called nonwoven materials, as innonwovens there is usually no crossing or entangling of the fibers, asis the case with webs or other, in particular textile tissues. In aspun-bonded nonwoven, in particular continuous filaments, which are alsoreferred to as filaments, are joined together to form the nonwoven,which is indicated in FIG. 1 by the irregular arrangement of the fibers1. Compared with known staple fiber nonwovens, the proposed nonwovens10, as indicated in FIG. 1, have advantages when used as filter media.

In a spin-blown process or a spun-bonding process, the nonwoven 10 isproduced by melting polymers and spinning them through a nozzle systeminto continuous filaments. These endless filaments are then exposed toan air stream which swirls the fibers or filaments. Subsequently, adeposition takes place to the web. Optionally, solidification methodscan then be used, so that a flat material is produced, for example, forfiltering particles in a gas stream.

The nonwoven material 10 shown in FIG. 1 comprises continuous fiberswhich are segmented. That is, a respective fiber, which may be referredto as a multi-component or poly-component fiber, is formed from a firstand a second plastic component. In the production process, the liquidplastic components are led separately through nozzles or holes andcombined to form a single continuous fiber.

In FIG. 2, an example of a multi-component fiber 1 is indicated. In theschematic illustration of FIG. 2, one can see a fiber 1 which has asheath surface 7 along its length extension Z. In FIG. 2, the fiber 1 isindicated in a preferred embodiment as a cylinder. In fact, the fiber 1,as indicated in FIG. 1, may have irregular bends and curves.

In FIG. 2, a cross-sectional area of the multi-component fiber 1 isvisible on the front side. It can be seen first pie segments 2, whichextend along the length Z of the fiber 1, and second segments 3, whichalso extend along the length Z. The segments 2 consist of a firstplastic component, and the segments 3, which are shown dotted, of asecond plastic component. Due to the nature of the production in thespin-blown process, molten plastic components nestle together ascontinuous filaments to the multi-component fiber 1. In the example ofFIG. 2, there are six segments which are arranged in the manner of piepieces in cross-section. They are also known as so-called segmented piefibers.

The two plastic components 2, 3, which are also referred to as segmentsbelow, lie side by side and adhere to one another. Along the lengthextension Z, there are outer segment boundaries 6 between the twoplastic components or the segments 2, 3. Since the multi-component fiber1 is formed as a solid material, internal segment boundaries 4 alsoresult between the segments 2, 3. Other geometries of multi-componentfibers are also conceivable. In addition to the pie segments, anexpression as a core-sheath structure with an additional plasticcomponent or one of the plastic components of the pie segments in theinterior of the fiber or a fiber with pie segments is also conceivable,which has a cavity inside, yet having outer segment boundaries presenton the outer surface.

FIG. 3 shows by way of example schematic cross-sectional views offurther exemplary embodiments. In FIG. 3A, the cross-section of amulti-component fiber 1, as indicated in FIG. 2, is shown incross-section. (Pie) segments 2 can be seen again in cross-section 3 ofa first plastic material and second segments 3 of a second plasticmaterial. The composition can be the same. The circumference of thefiber 1 is denoted by 5. In FIG. 3A, six segments are indicated with sixouter boundary lines 6. Of these, only one is provided with referencenumerals for the sake of clarity. It is also possible to providemulti-component fibers with a different segmental division. For example,juxtaposed segments can be created so that outer segment boundariesresult at the resulting sheath surface.

FIG. 3B shows a multi-component fiber 1′ in cross-section having foursegments 2, 3. In the production, for example, four nozzles are combinedin a spinning beam in such a way that fibers with a correspondingcross-section are formed.

In FIG. 3C, yet another multi-component fiber 1″ is indicated incross-section. The multi-component fiber 1″ has eight segments 2, 3 andaccordingly also eight outer segment boundaries 6. The diameter of thefiber is denoted by D. The multi-component fiber 1″ has, for example, adiameter of 10 μm. In known spun-bonded nonwovens, the segments 2, 3 aresplit after the production of the continuous filaments in order toproduce smaller or thinner fibers. This is not desired in the nonwovenmaterial proposed herein and is therefore rather or even as far aspossible avoided. In the nonwoven material 10 shown in FIG. 1, thefibers retain their segmented composition, i.e., the fibers aresubstantially non-split.

FIGS. 4A to 4C show scanning electron micrographs of sections of suchspun-bonded nonwovens for use as a filter medium. The plastic componentsof the fibers in region I shown in FIG. 4 are both formed from athermoplastic polyolefin provided with a lower meltable additive. Thesegments 2, 3 can be seen on the marked fiber in cross-section on theexample of FIG. 4A. The representation essentially corresponds to theschematic representation, as it is indicated in FIG. 3C, in which casethe segments 2 are smaller than the segments 3. There are 16 segments intotal in FIG. 4A which are visible. Grooves 6′ can be seen along thelength extension of the respective peripheral surface at the outersegment boundaries 6 of the fibers 1. The diameter D of the fiber isabout 30 μm. The fibers 1 indicated in FIG. 4A are solidified into aspun-bonded nonwoven. In other words, the web, which was deposited bythe spin-blown process, is thermally treated in such a way that, at theboundary points 8 or contact surfaces between separate fibers, they arefused together. This is indicated by the arrows 8 in FIG. 4A. It can beseen in particular in the lower marked area II, as the two adjacentfibers or segments are fused together.

The thermoplastic polypropylene material used for the preparation isthus provided with an additive, for example, a polypropylene metallocenehomopolymer, which has a lower melting point than the base propylene.For example, the polypropylene PPH 9099 can be used, available fromTotal Research & Technology, Feluy, which is a homopolymer, and asadditive, a polypropylene available under the name Lumicene MR 2001 fromthe same manufacturer can be used. To adjust the melting point, it isalso conceivable to use a polypropylene copolymer, for example Adflex Z101 H, which is available from LyondellBasell Industries Holdings B.V.

It is possible to perform differential scanning calorimetry on thefibers to detect, for example, two different melting points. In acorresponding investigation, which is also referred to as DDK analysisor differential scanning calorimetry (DSC) analysis, a thermal analysisis carried out to measure the amount of heat emitted or absorbed by asample during heating, cooling or an isothermal process. The sample is,for example, a certain amount of the spun-bonded nonwoven. By means ofDDK analyzes in accordance with DIN EN ISO 11357-1, several meltingpoints or melting temperatures of the polymer mixtures can be detected.

As a result of using corresponding thermoplastic materials as plasticcomponents, spun-bonded nonwovens, as shown in FIGS. 4A to 4C, can firstbe simply spun and then solidified. FIG. 4B shows another spun-bondednonwoven as an SEM (Scanning Electron Microscope) image. The diameter Dof the fibers is less than shown in FIG. 4a , and is about 10 to 15 μm.In the marked area III, it can be seen how three of the endless fibersstick together and yet are completely non-split. The choice of materialsand the production ensures that the fibers are as non-split as possible.Outer segment boundaries can also be seen in FIG. 4B extending along thefibers 1 emerging as grooves 6′.

FIG. 4C shows a further section of a fabric material with even thinnermulti-component fibers 1. Also in FIG. 4C, it can be seen how the fibers1 were solidified together by thermal exposure. That is, at theinterface between the fibers 1, the materials are fused together.

Compared to fabric materials formed from split multi-component fibers,the multi-component fibers proposed herein have a relatively smoothsurface. However, for example, due to the thermal treatment on thesheath surfaces, grooves are formed between segments by the materialtransition. Along a circumference 5 (see FIG. C) of a correspondingmulti-component fiber 1, a certain roughness is created through thegrooves 6′. This is indicated schematically in FIG. 5.

FIG. 5 shows a diagram in which the circumference U of a singlemulti-component fiber is indicated on the x-axis and the respectiveradius r on the y-axis. The radius r has 6 minima at the locations ofthe outer segment boundaries and deviates from the average radius D/2.It is thus possible to indicate a roughness along a respectivecircumference of a fiber.

A possible measure of the roughness or smoothness of the sheath surfacealong a circumferential line is the average roughness depth Rz. In theinvestigated multi-component fibers, the average roughness depth Rz isless than 2 μm. For example, the average surface roughness Rz can bedetermined according to ISO 4287/1. For example, a circumferential lineof a fiber is considered as a measuring section. The circumference isthen divided into

seven individual measuring sections, whereby the middle five measuringsections are selected to be the same size. For each of these individualmeasuring sections, the difference between the maximum and minimumvalues is determined on the circumference of the profile.

Partially Split Multi-Component Fibers

In FIG. 5, the minima and maxima of the radius would result in arespective minimum and maximum. The mean value is then formed for thesedetermined single roughness depths. Due to the relatively smooth surfaceof the sheath surface 7 in the multi-component fibers 1, this averageroughness depth is rather low. The spun-bonded nonwovens usable asfilter medium (see FIG. 1) are the multi-component fibers preferablynon-split and have a rather smooth peripheral line or sheath surface.

The known applications of segmented pie or otherwise differentlymulti-component segmented fibers require splitting them into thesegments in order to achieve smaller fiber units. This is done forexample by an influence of a water jet. They are also known as ahydrodynamic needling of corresponding fragmentary fibers. Usually, asexplained in US 2002/0013111 A1, certain polymer materials are used forthe various segments, which enable easy splitting after the spinningprocess. For example, polyester materials having aromatic or polylacticacid moieties are known.

The investigations of the applicant have revealed that thermoplasticpolymer materials, such as polyolefins, and in particularpolypropylenes, are particularly well suited to produce multi-componentfibers which are less split and are also particularly resistant to knownsplit processes. It can already be seen in FIGS. 4A to 4C that even inthe thermally solidified state, the multi-component fibers have coherentsegments. Preferably, the proportion of partially split fibers is small.

In FIG. 6, for example, a fiber is indicated schematically. The darkcurves represent contiguous segments 2, 3 of a multi-component fiber 1.The length extension of the multi-component fiber 1 is indicated by Z.It can be seen in a length range Z1 that the segments 2/3 are stucktogether and non-split. These segments are indicated with 2/3. As aresult of impacts during the production process or during the furtherprocessing of the nonwoven materials, the fibers can basically split up.This means that individual segments are formed, which are detached fromthe rest. This is designated in section Z2 by 2′/3′.

In the example of FIG. 6, the ratio between the portion Z1 and theportion Z2 may be selected as a measure for splitting on the one hand orfor a non-split length fraction of a fiber. Assuming that the totallength of the examined fiber is Z1+Z2, there is a length fraction of themulti-component fiber 1 of Z1/(Z1+Z2) in which the segments 2, 3 of themulti-component fiber are not split or separated. In the example of FIG.6, approximately 60% length fraction is seen to be non-split.Conversely, the length fraction of the multi-component fiber 1 indicatedin FIG. 6, in which the pie segments 2′/3′ of the fiber is split fromeach other, is at about 40%. Preference is given to filter media inwhich the spun-bonded nonwoven is composed of as many non-splitmulti-component fibers as possible.

A corresponding determination of the length fraction of one or moremulti-component fibers which are not split can be effected, for example,by a sample of a predetermined section, for example 1 mm² or 1 cm², ofthe flat spun-bonded nonwoven.

An alternative way of determining the splitting portion in a spun-bondednonwoven of multi-component fibers may be the proportion ofmulti-component fibers in a sample that are non-split. For example, thespun-bonded nonwovens shown in the cutouts in FIGS. 4A to 4C are formedalmost entirely of non-split multi-component fibers. A multi-componentfiber can be classified as split if several segments detach, as is thecase in the length range Z2 of the fiber 1 of FIG. 6, for example. Forexample, in a volume or area section of a spun-bonded nonwoven, theproportion of multi-component fibers having split-off or split segmentscan be counted. This is preferably not more than 50%.

The more non-split multi-component fibers exist in the spun-bondednonwoven, the better the filtration properties. What is desired is avery high proportion of multi-component fibers, in which the segmentsare connected to one another along their segment boundaries in thelength extension.

Steps in the Production Process of the Spun-Bonded Nonwoven

FIGS. 7 and 8 schematically show method steps in a production method fora filter medium made of a spun-bonded nonwoven. In FIG. 7, the steps areshown in order to produce a web from first and second plasticcomponents, and in FIG. 8, the processes for forming a solidified filtermedium from the web are indicated.

In a first step, the starting materials for the first plastic componentand the second plastic component are provided. This is indicated in FIG.7 by method steps S1 and S2. In the exemplary embodiment of a productionmethod indicated below, the first component and the second componenthave a different composition. For example, the starting material of thefirst plastic component is a thermoplastic polyolefin. In particular,the PPH 9099 polypropylene available from Fa. TOTAL has proven to besuitable. PPH 9099 is a homopolymer polypropylene with a melting pointof 165° C. More characteristics of possible thermoplastic polyolefinsAM, MB, MC are shown in this table.

TABLE 1 Melting point Melt Flow (ISO Index Name Manufacturer Type 3146)(ISO 1133) MA PPH 9099 Total ho-PP 165° C. 25 g/10 min MB Lumicene Totalm-PP 151° C. 25 g/10 min MR2001 MC Adflex Z101H LyondellBasell co-PP142° C. 27 g/10 min

The starting material of the second component is chosen to have a lowermelting point. For this purpose, for example, several portions ofthermoplastic polyolefins can be used. A mixture of a polypropyleneavailable from Fa. TOTAL has proven to be suitable under the namesLumicene MR 2001, in the following MR2001. The melting point is 151° C.MR 2001 is a metallocene homopolymer made from polypropylene. The secondcomponent may be added to another polypropylene, such as, for example,the Adflex Z 101 H available from LyondellBasell, hereinafter Adflex,having a melting point of 142° C. The mass fraction of the startingmaterials of the first component with the second component is, forexample, 70% to 30%. For the first component, which consists of a singlethermoplastic material, for example the aforementioned PPH 9099, one canalso speak of a base material.

The mass ratio between the ratio of MR 2001 to Adflex Z 101 H in thestarting material of the second component is, for example, about 75 to25%. In this case, the starting materials can be prepared by mixingappropriate granules of the thermoplastic materials.

The starting materials of the first and second components arecorrespondingly metered in steps S1 and S2 and fed to an extrusiondevice in step S3. The molten starting materials are fed by means of anextruder in step S3 to a bonding beam with corresponding nozzles forforming the segment geometry. Optionally, filters and pumping devicesmay be present in the stream of the liquefied respective thermoplasticpolymer.

In step S4, a spun-bonding or spin-blown process is carried out in whichendless filaments with the segmented pie structures are formed from thenozzles. From the spinning process, in step S4, segmented pie filamentsare obtained from the first and second plastic components. By an airstream effect, the filaments are stretched and swirled and thendeposited in particular on a screen belt. This is indicated in themethod steps S5, S6 and S7.

The stretching S5 is done by a suitable primary air supply, and theswirling S6 downstream in the manufacturing process by secondary air.This results in a web during the dropping S7 of segmented filaments,which can also be referred to as multi-component filaments. Theresulting web then has a thickness of between 1 and 2 mm.

In an optional step, it is possible to thermally pre-solidify the web bysucking the filaments on the one hand through the filing screen orscreen belt, and on the other hand by solidifying or pre-solidifyingwith the aid of, for example, hot air or other thermal exposure. One cancall this web a semi-finished product that already has spun-bondednonwoven properties. In principle, this semi-finished product canalready be used for filtering fluids.

In order to achieve an even better, also mechanical, property of thespun-bonded nonwoven from multi-component segmented pie filaments, afurther solidification takes place. This is indicated schematically inFIG. 8. The pre-solidified web is guided in a bonding or solidificationstep S9 between spaced screen belts, rolls or rollers and simultaneouslyexposed to a temperature which is higher than the melting temperature ofat least one of the two plastic components. For example, when using thepolypropylene materials previously listed in the table, thermal bondingcan occur at temperatures between 150 and 158° C. The thermallysolidified spun-bonded nonwoven then has a thickness of between 0.5 and1.5 mm, for example. The thickness can be adjusted by the spacing of thescreen belts or heatable rolls or rollers.

In the proposed production method, in particular no apparatus forhydrodynamic solidification, needling or chemical solidification orbonding are used. This reduces the amount of split multi-componentfibers in the spun-bonded nonwoven.

In a subsequent step S10, the solidified spun-bonded nonwoven ischarged. Charging takes place, for example, with the aid of wire or rodelectrodes, which opposite rollers, over which the flat and rollablespun-bonded nonwoven is guided. In particular, an apparatus and acharging method can be used for this purpose, as explained in U.S. Pat.No. 5,401,446. U.S. Pat. No. 5,401,446 is hereby incorporated byreference (“incorporation by reference”). Investigations by theapplicant have shown that, in particular, a stage charge, as shown forexample in FIG. 1 of U.S. Pat. No. 5,401,446, is favorable with the aidof two successively connected charging drums and charging electrodes.

Subsequently, the obtained charged spun-bonded nonwoven is provided as afilter medium, for example, in roll form (step S11). Throughout theentire production path of the spun-bonding process, the multi-componentfibers remain non-split or largely non-split. In the case of thermalsolidification in step S9, for example, only a part of the thermoplasticmaterial is melted from the starting materials and leads to theinterconnection of different multi-component fibers.

The flat filter medium of a single-layer spun-bonded nonwoven is nowprovided in particular in roll form. High quality filter media can beachieved from the sheet material due to the filtration properties, butalso due to the mechanical handling in terms of its flexural rigidity.

Comparison of the Mechanical Properties of the Filter Medium withComparative Nonwovens

The applicant has carried out comparative investigations, for example onthe flexural rigidity of spun-bonded nonwovens made according to theproposed method, with materials processed in commercially availablefilter elements. A filter element of the type CU 3054 distributed by themanufacturer MANN+HUMMEL GmbH was examined. In the following

table, the flexural rigidities of a test nonwoven are compared withthose of comparative nonwovens. Commercially available filter elementsare partly manufactured with filter medium from different manufacturers.Comparative nonwovens 1, 2 and 3 are based on commercially availablefilter media for interior filters.

TABLE 2 Flexural rigidity according to DIN 53121 Sample Type Front BackMedium Test nonwoven 1 Spun-bonded 210 mN 219 mN 214.5 mN nonwovenComparative Meltblown 157 mN 165 mN   161 mN nonwoven 1 ComparativeMeltblown 149 mN 149 mN   149 mN nonwoven 2 Comparative 2-ply  63 mN  51mN    57 mN nonwoven 3

The test nonwoven 1 used two plastic components. Three thermoplasticmaterials MA, MB and MC were used, with MA PPH 9099, MB MR2001 and MCAdflex being chosen. The first plastic component essentially comprisesMA. The second plastic component essentially comprises a mixture of MBand MC in the ratio 3:1. Overall, the mass ratio in the fiber is: MA:70%, MB: 22.5% and MC: 7.5%. A spun-bonded nonwoven of the grammage or aweight per unit area of 100 g/m² was produced and investigated using asystem available from Reifenhauser Reicofil as test nonwoven 1. Thethickness of the spun-bonded nonwoven was 1.14 mm with a weight of 106g/m². The measurements were carried out according to DIN 29076-2 or DIN29073-1. There were sixteen pie segments in the fibers.

The comparative nonwoven 1 can be used for a commercial filter elementCU3054 of the manufacturer MANN+HUMMEL GmbH and is made of apolypropylene with a grammage of 125 g/m² and has a thickness of 1.25mm.

The comparative nonwoven 2 can be used for a commercial filter elementCU3054 of the manufacturer MANN+HUMMEL GmbH and is made of apolypropylene with a grammage of about 146.5 g/m² and has a thickness ofabout 1.15 mm.

The comparative nonwoven 3 can be used for a commercial filter elementCU3054 of the manufacturer MANN+HUMMEL GmbH and is made of a two-plypolyester/polypropylene material with a grammage of about 105 g/m² andhas a thickness of 0.6 mm. The carrier layer made of polyester isprovided with a meltblown layer of polypropylene.

It can be seen that, compared to conventional comparative media basedeither on spun-bonded or multilayered materials, they have improvedflexural rigidity. This allows a particularly good further processing,for example in filter elements made of zigzag-pleated filter media.

Possible Additional Equipment of Filter Media

In FIG. 9, a further embodiment for a filter medium 11 is indicated. Theembodiment comprises a first filter layer 9, for example of a meltblownmaterial, onto which a spun-bonded nonwoven 10 is applied, which iscomposed essentially of non-split multi-component fibers.

In order to further improve or change the filtration properties, it ispossible, as indicated in FIG. 10, to embed adsorbent particles 13 in orbetween layers of filter media. For example, the filter medium 12 has afirst layer of a meltblown material 9 and a second layer of thedescribed spun-bonded nonwoven 9′. In between, for example, adsorberparticles 13 of activated carbon or other adsorbent agents are embedded.As a result, volatile hydrocarbons, for example, can be retained inaddition to particle filtration when the filter medium 12 passesthrough.

Filtration Properties of Filter Media

The applicant has produced further test webs and examined theirproperties. In the following table 3, the thicknesses, the airpermeability, the grammage and the flexural rigidity are shown for testnonwovens 1 to 4.

TABLE 3 Thickness Air permeability Grammage Sample (DIN 29076-2) (DIN9237) (DIN 29073-1) Test nonwoven 2 0.86 mm 4,500 I/m²s  88 g/m² Testnonwoven 3 0.90 mm 2,323 I/m²s  90 g/m² Test nonwoven 1 1.14 mm 1,809I/m²s 106 g/m² Test nonwoven 4 1.18 mm 1,705 I/m²s 124 g/m²

For the test nonwovens 2, 3 and 4, the same starting material was usedas for the test nonwoven 1 for the two plastic components of thesegments.

Table 4 lists the filtration properties of the test nonwovens.

TABLE 4 NaCl ISO A2 ISO A2 ISO A2 deposition initial initial dustefficiency separation separation retention at 0.3 μm at 1 μm at 5 μmcapacity at (DIN (DIN (DIN 50 Pa (DIN Sample 71640-1) 71460-1) 71460-1)71460-1) Test   24%   80%   87%   65 g/m² nonwoven 2 Test   43%   88%  95%   34 g/m² nonwoven 3 Test 47.3% 94.4% 97.5% 36.2 g/m² nonwoven 1Test   52%   93%   98%   34 g/m² nonwoven 4

Pleated Filter Media and Filter Elements

In the following FIG. 11, a zigzag-pleated medium is shown as a pleatpack 20. The filter medium 10 accordingly has pleats 21, which typicallyextend transversely to the machine direction M. The pleated filtermedium is also referred to as a pleat pack 20 or pleated. The pleats 21may be produced by pleating along sharp pleat edges 22 (also referred toas pleat tips) or by a wavy embodiment of the filter medium 10. Arespective pleat 21 may be defined by two pleating sections 23, whichare connected to one another via a corresponding pleating edge 22.According to the exemplary embodiment, the pleated edges 22 point in oragainst the direction of flow, which is indicated in FIG. 11 by thearrow L.

A pleat in which the pleats 21 have a varying height H is also possible.Further, the pleat spacing between the pleats 21 may vary so that thedistance D₁ is not equal to the distance D₂. The pleat pack 20 may bedesigned to be self-supporting, i.e. the pleats 21 are dimensionallystable in the case of an intended flow in the filter operation.

The filter medium 10 used is limited in the machine direction M by endpleats 30, 31. Transverse thereto, the filter medium 10 is bounded bypleat end edges 19, 20 (also referred to as pleat profiles 33). “Pleatend edge” refers to the end face pleat surface which extends betweenadjacent pleat edges 33 of a respective pleat 22.

The filter medium 10 may have a rectangular shape in plan view, that is,in the plane E of its planar extension. However, a triangular,pentagonal or polygonal, round or oval shape is also conceivable.

One possible application is the use of the respective filter medium ininterior air filters for motor vehicles. FIG. 12 shows a motor vehicle14 with an air conditioner 15, which may be formed as a heating airconditioner. The air conditioner 15 receives outside air 16 and suppliesfiltered air 17 to a cabin 18 (also referred to as a passengercompartment) of the motor vehicle 14. For this purpose, the airconditioner 15 comprises a filter arrangement shown in FIG. 13.

The filter arrangement 24 comprises a filter housing 19 with an interiorfilter 32 accommodated therein, in particular exchangeably. The interiorfilter 32 is shown in more detail in FIG. 14. The interior filter 32comprises a filter medium pleated as a pleat pack 20 (see. FIG. 11),which in particular is all around connected to a frame 25. The frame 25may include, for example, sidebands 26, 27 and headbands 28, 29.

The sidebands 26, 27 shown in FIG. 14 are connected to the pleat endedges 33, the headbands 28, 29 to the end pleats 30, 31, in particularby fusing, abrasing or gluing. The sidebands 26, 27 and the headbands28, 29 may form the frame 19 in one piece or in several parts. Thesidebands 26, 27 and the headbands 28, 29 can be made, for example, froma particularly flexible fiber material or as in particular rigidsynthetic injection molded components. In particular, the frame 19 maybe produced by injection molding on the pleat pack 20.

In filter operation, the filter medium 10, as shown in FIG. 11 or 13,flows perpendicular to its flat extent of air L. The air L flows from araw side RO of the cabin air filter 8 toward a clean side RE thereof.

In order to ensure a sufficient seal between the raw and clean sides RO,RE, a seal between the cabin air filter 32 and the filter housing 19 maybe provided. The seal may, for example, be integrated in the frame 25.In this case, the frame 25 is at least partially formed of a sealingmaterial. Alternatively, the seal can be provided as an additional part,for example, attached, in particular be molded, onto the frame 25.

The filter element 32 reproduced in FIG. 14 surrounds a cuboidal volumewith the boundary surfaces A₁, A₂, A₃. The largest boundary surface A₁corresponds to the outflow or inflow side of the filter element 32.

Filtration Properties of the Pleat Pack

The applicant has carried out comparative investigations in which priorart filter elements, namely CU 3054 interior air filter elementsmanufactured by MANN+HUMMEL GmbH, have been compared with filterelements of identical geometrical design. The comparison and test filterelements have a shape as shown in FIG. 14. The test filter elements areequipped with a respective spun-bonded nonwoven made of multi-componentfibers produced by the method proposed herein. The spun-bonded nonwovenswere solidified and subjected to a charge. For this purpose, threeelectrode arrangements each having a voltage between the electrode andthe winding roll of 25-35 kV have been used. The distance to thespun-bonded nonwoven was about 20 to 40 mm, and the running speed alongthe electrode assemblies was between 30 and 40 m/min. The flatspun-bonded nonwoven present as rolled goods was then subjected tozigzag pleating and provided with sidebands and headbands according toCU 3054.

Each filter element tested has a length extension of 292±1.5 mm, a widthof 198.5±1 mm and a height of 30±1 mm. This results in pleat heightsH=28 mm with a total of 42 pleats in the resulting pleat pack. The pleatspacing D₁=D₂ is 7 mm. The filter area is thus 0.466 m² for a cover areaA₁ of the filter element of 0.058 m² (see FIG. 9, 14). The commerciallyavailable filter elements are available with different retentioncapacities. In the commercial comparative filter elements, a filtermedium is used, made of a meltblown nonwoven. Alternatively, a two-plymaterial of high retention polyester and polypropylene can be used.

FIG. 15 shows curves from pressure drop measurements of a test pack 3for the filter grade D and a commercial filter element CU 3054 having aconventional filter medium. Over the entire volume flow range of 100 to600 m³/min, the filter element with a pleat pack of multi-componentspun-bonded fibers substantially non-split in the filter element (Testpack 3) provides better results than the prior art filter medium(Comparison pack 3).

From the following table, it can be seen that the proposed single plyspun-bonded nonwovens of propylene blends result in improved rates ofseparation and improved pressure drops. All measurements were carriedout in accordance with DIN 71460-1.

TABLE 5 Pressure NaCl ISO A2 ISO A2 drop deposition initial initial at600 efficiency separation separation Sample m³/h at 0.3 μm at 1 μm at 5μm Comparison  39 Pa 12% 46% 66% pack 1 Test pack 1  36 Pa 24% 79% 86%Comparison  58 Pa 20% 69% 94% pack 2 Test pack 2  55 Pa 39% 92% 96%Comparison 137 Pa 54% 95% 99% pack 3 Test pack 3  77 pa 49% 95% 98%

In this respect, a filter element made from the proposed spun-bondednonwoven is superior to the known filter element materials. This appliesin particular with regard to the flexural rigidity of the filter medium,the retention capacity and the dust storage capacity. The higher therequirements for filter media and filter elements, the better theproposed spun-bonded non-spliced multi-component fibers.

REFERENCE SIGNS USED

-   1 Multi-component fiber-   2, 3 Segments/plastic component-   4 Inner segment boundary-   5 Circumference-   6 Outer segment boundary-   6′ Longitudinal groove-   7 Sheath surface-   8 Junction-   9 Meltblown material-   10 Spun-bonded nonwoven-   11 Filter medium-   12 Filter medium-   13 Adsorber particles-   14 Motor vehicle-   15 Air conditioner-   16 Outside air-   17 Filtered air-   18 Interior-   19 Filter housing-   20 Pleat pack-   21 Pleat-   22 Pleat edge-   23 Pleat section-   24 Filter arrangement-   25 Frame-   26 Sideband-   27 Sideband-   28 Headband-   29 Headband-   30 End pleat-   31 End pleat-   32 Interior air filter-   33 Pleating profile-   D₁, D₂ Pleating distance-   A₁, A₂,-   A₃ Boundary surface-   E Level-   H Pleat height-   L Air flow-   M Machine direction-   U Circumference-   D Diameter-   Z Length extension-   RO Raw air area-   RE Clean air area

What is claimed is:
 1. A filter medium (10) for filtering a fluid foruse in an interior air filter (32), comprising: a spun-bonded nonwovenwhich is formed at least partially from multi-component segmented piefibers (1) having at least a first plastic component (2) and a secondplastic component (3), wherein a portion of multi-component fibers (1)whose pie segments (2, 3) are interconnected at inner segment boundaries(4) of the multi-component fibers (1) along their length extension (L),is at least 50%.
 2. The filter medium of claim 1, wherein themulti-component fibers (1) have a pie-shaped cross-section.
 3. Thefilter medium according to claim 1, wherein a respective multi-componentsegmented pie fiber (1) has a sheath surface (7), and the plasticcomponents (2, 3) adjoin one another on the sheath surfaces (7) of themulti-component fibers (1).
 4. The filter medium of claim 3, wherein thesheath surface (7) has longitudinal grooves (6′) along boundary surfaces(6) between the plastic components (2, 3).
 5. The filter mediumaccording to claim 3, wherein the sheath surface (7) along itscircumference (5) has an average roughness depth (Rz) of less than 2 μm.6. The filter medium according to any of claim 1, wherein themulti-component segmented pie fibers (1) have an average diameter (D) ofat least 10 μm.
 7. The filter medium according to claim 1, wherein themulti-component segmented fibers (1) have at least four pie segments (2,3).
 8. The filter medium according to claim 1, wherein the plasticcomponents (2, 3) of the multi-component fibers (1) do not split apartunder the influence of a water jet treatment.
 9. The filter mediumaccording to claim 1, wherein the proportion of multi-component fibers(1) in which the pie segments (2, 3) are joined together at the innersegment boundaries (4) of the multi-component fibers (1) along theirlength extension (L) is at least 70%.
 10. The filter medium according toclaim 1, wherein when a length fraction of the multi-component fibers(1) of not more than 50%, the pie segments (2, 3) of the multi-componentfibers (1) are split from one another.
 11. The filter medium accordingto claim 1, wherein the spun-bonded nonwoven (1) has a machine direction(M), and the multi-component fibers (1) are oriented along the machinedirection (M).
 12. The filter medium according to claim 1, wherein theplastic components (2, 3) are partially fused together in areas of theboundaries (4, 6) between the first and the second plastic component (2,3).
 13. The filter medium according to claim 1, wherein themulti-component fibers (1) are interconnected exclusively by hot airbonding.
 14. The filter medium according to claim 1, wherein thespun-bonded nonwoven (10) has a thickness (D) of between 1.0 mm and 2.0mm.
 15. The filter medium according to claim 1, wherein themulti-component fibers (1) are thermally interconnected or thermallybonded together to form a nonwoven.
 16. The filter medium according toclaim 1, wherein the spun-bonded nonwoven (10) has a thickness ofbetween 0.5 mm and 1.5 mm.
 17. The filter medium according to claim 1,wherein the plastic components (2, 3) of the multi-component fibers (1)are charged as electrets.
 18. The filter medium according to claim 1,wherein the spun-bonded nonwoven (10) has a grammage of between 80 g/m²and 160 g/m².
 19. The filter medium according to claim 1, wherein thefilter medium (11) further comprises a meltblown material (9).
 20. Thefilter medium according to claim 1, wherein the first plastic component(2) and/or the second plastic component (3) consist of a polypropylene.21. The filter medium according to claim 1, wherein the first plasticcomponent (2) has a first melting point (T2); and the second plasticcomponent (3) has a second melting point (T3); wherein the first meltingpoint (T2) is higher than the second melting point (T3) by at least 8degrees K.
 22. The filter medium according to claim 1, wherein a massfraction of the first plastic component is between 20% and 80%.
 23. Thefilter medium according to claim 1, wherein the first plastic component(2) and/or the second plastic component (3) has/have a first portion ofa first thermoplastic material (MA) having a first melting point (TA)and a second portion of a second thermoplastic material (MB) having asecond melting point (TB); wherein the first melting point (TA) ishigher than the second melting point (TB).
 24. The filter mediumaccording to claim 23, wherein the second thermoplastic material (MB) ofdifferent multi-component fibers (1) is partially fused together tosolidify the spun-bonded nonwoven (10).
 25. The filter medium accordingto claim 24, wherein the first thermoplastic material (MA) is apolypropylene homopolymer and/or the second thermoplastic material (MB)is a metallocene polypropylene.
 26. The filter medium according to claim23, wherein a mass fraction of the first thermoplastic material (MA)between 70% and 95%.
 27. The filter medium according to claim 23,wherein the first thermoplastic material (MA) and/or the secondthermoplastic material (MB) has/have a melt flow index (MFI) of between20 g/10 min and 30 g/10 min.
 28. The filter medium according to claim 1,wherein the spun-bonded nonwoven (10) is thermally solidified in arespective area of 10 cm² in such a way that the spun-bonded nonwoven(10) is self-supporting.
 29. The filter medium according to claim 1,wherein the spun-bonded nonwoven (10) has an air permeability of between1,300 l/m²s and 1,700 l/m²s.
 30. The filter medium according to claim 1,wherein the spun-bonded nonwoven (10) has a NaCl retention capacity at0.3 μm of greater than 20%.
 31. The filter medium according to claim 1,wherein the spun-bonded nonwoven (10) has a dust storage capacity at 50Pa of more than 20 g/m².
 32. The filter medium according to claim 1,wherein the spun-bonded nonwoven (10) has a flexural rigidity in themachine direction (M) of more than 170 mN.
 33. The filter mediumaccording to claim 1, wherein the spun-bonded nonwoven (10) comprisespleats (21) with a plurality of pleat sections (23) arranged betweenpleat edges (22).
 34. The filter medium of claim 33, wherein the pleats(21) extend transversely to a machine direction (M).
 35. A method ofproducing a filter medium according to claim 1, the method comprisingthe steps: spinning the multi-component fibers (1) of the spun-bondednonwoven (1) by a spinnerette; cooling the multi-component fibers;depositing the multi-component fibers on a storage screen band toproduce a fabric web of the spun-bonded nonwoven; performing a firstsolidification stage of the nonwoven web by applying heated air;performing a second solidification stage in a double belt furnace,flatly by heated air application; wherein in the second solidificationstage, a surface pressure on the fabric web at the same time.
 36. Themethod according to claim 35, wherein a flat pressure is applied to thefabric web at a pressure of between 5 and 15 Pa; and/or the firstsolidification stage is carried out in the storage screen band.
 37. Themethod according to claim 36, wherein in the first solidification stage,a fluid temperature is used which is below the melting point of thecomponent with the highest melting point of the multi-component fibers(1) and above the lower melting point of the multi-component fibers (1)such that the multi-component fibers (1) are melted or fused.
 38. Afilter element (32), comprising: a spun-bonded nonwoven which is atleast partially formed from multi-component segmented pie fibers (1)having at least a first plastic component (2) and a second plasticcomponent (3), wherein a portion of multi-component fibers (1) whose piesegments (2, 3) are interconnected at inner segment boundaries (4) ofthe multi-component fibers (1) along their length extension (L), is atleast 50%.
 39. The filter element according to claim 38, wherein aportion of the multi-component segmented pie fibers (1) on thespun-bonded nonwoven is greater than 50%.
 40. The filter element (32)according to claim 39 having a filter medium according to claim 1 whichis pleated in a zigzag to form a pleat pack (20).
 41. The filter elementaccording to claim 40, further comprising: sidebands (26, 27) attachedto opposite pleat profiles of the pleat pack (20); and headbands (28,29) attached to opposite end pleats (30, 31) of the pleat pack (20). 42.The filter element according to claim 41, wherein the filter element(32) is an interior air filter element for a motor vehicle (14).
 43. Thefilter element according to claim 41, wherein outer boundary surfaces(A1, A2, A3) of the pleat pack (20) include a cuboidal volume and atleast two opposing boundary surfaces, each having an area between 0.05and 0.066 m2.
 44. The filter element according to claim 42, wherein thefilter medium (10) has an filtration area between 0.458 and 0.472 m².45. The filter element according to claim 41, wherein the pleat pack(20) in a machine direction (M) has a length of between 285 and 300 mmand between 38 and 46 pleats (21), the pleat heights (H) being between25 and 31 mm.
 46. The filter element according to claim 41, wherein thefilter element (32) comprises an adsorbent layer.
 47. The filter elementaccording to claim 41, wherein the filter element (32) is treated withflame resistant additives or flame retardants.
 48. The filter elementaccording to claim 41, wherein the filter medium (10) is adapted forfiltering a particle loaded gas stream.